Generators are based on the principle of electromagnetic induction, which was discovered by Michael Faraday in 1831. Faraday discovered that when an electrical conducting material (such as copper) is moved through a magnetic field (or vice versa), an electric current will begin to flow through that material. This electromagnetic effect induces voltage or electric current into the moving conductors.
Current power generation devices such as rotary alternator/generators and linear alternators rely on Faraday's discovery to produce power. Typically, rotary generators are essentially very large quantities of wire spinning around the inside of very large magnets. In this situation, the coils of wire are called the armature because they are moving with respect to the stationary magnets (which are called the stators). Typically, the moving component is called the armature and the stationary component is called the stator.
Linear generators, in contrast, usually have a magnetic core moving through coils of wire. As the magnetic core passes through the coils, electrical current is produced. In this situation, the magnetic core is the armature because it moves relative to the coils, which are now called the stators.
Typically, some energy source is used to provide power to move the armature with respect to the stator. Typical sources of mechanical power are a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, or even a hand crank.
As the energy sources for the country and the world grow more scarce, there is a need for more efficient methods and mechanisms for producing electric power. Furthermore, not all sources of mechanical power are readily available in all areas of the world, so there is also a need for methods and mechanisms that produce electrical power from readily-obtainable power sources such as wind and waves.